Structural health monitoring (SHM) is a method of determining the health of a structure from the readings of an array of permanently-attached sensors that are embedded into the structure and monitored over time. SHM can be performed in two basic ways, passively and actively. Passive SHM corresponds to monitoring a number of structure related parameters including, but not limited to, loading stress, environment action, performance indicators, acoustic emission from cracks, and inferring the state of structural health from a structural model. In contrast, active SHM performs proactive interrogation of the structure, detects damage, and determines the state of structural health from the evaluation of damage extend and intensity. Both approaches aim at performing a diagnosis or analysis of the structural safety and health, to be followed by a prognosis of the remaining life. Passive SHM uses passive sensors which only “listen” but do not interact with the structure. Therefore, they do not provide direct measurement of the damage presence and intensity. Active SHM uses active sensors that interact with the structure and thus determine the presence or absence of damage. The methods used for active SHM resemble those of nondestructive evaluation (NDE), e.g., ultrasonics, eddy currents, etc., only that they are used with embedded sensors. Hence, active SHM could be seen as a method of embedded NDE. One widely used active SHM method employs piezoelectric wafer active sensors as described, for example, in U.S. Pat. No. 7,024,315, which discloses sending and receiving Lamb waves to determine the presence of cracks, delamination, de-bonding, and corrosion. Due to its similarities to NDE ultrasonics, this approach is also known as embedded ultrasonics.
In order to thoroughly investigate the state of health of structural components, different methods are needed. Impedance is useful to detect corrosion, pitch-catch and pulse-echo are used to detect through the thickness damage, and phase-array is used for non-destructive evaluation methods (NDE). After data collection is performed, the data must be analyzed. Each method requires a different approach for data analysis. Different hardware and software are available for data processing, but often the data must be manually transformed to be used in the software. In order to make the SHM process smoother and quicker, both integrated hardware components and integrated software to collect, process, and display the results are needed.
A structural component can deteriorate or brake for different reasons. Corrosion on metallic structures reduces the thickness of the component and hence its ability to sustain load. If the thickness goes below a critical value, the structure is no longer able to resist the design load and will eventually brake. Cracks in metallic structure can lead to catastrophic failures due to either fatigue load or static load. Composite structures can fail because of delamination, de-bonding, or because of impact damages. The SHM operator must use different kinds of methods to determine whether a structure is healthy or not.
Wave propagation is often used for crack and delamination, but different damage locations in the thickness of the structure requires different wave modes. Electromechanical (E/M) methodologies may be used for corrosion detection and to test the integrity of the sensor-to-structure bonding. Each method requires a different hardware component with a corresponding dedicated software component. After data collection is performed the operator must format the collected data to the specific data analysis software to derive conclusions on the health of the structure. The entire process can be confusing and can easily lead to errors and missing data. Moreover it is time consuming and memory consuming because the data are often duplicated to adapt to the format of the data analysis software.
In order to develop any of the SHM technique several sensors are needed. During data collection several piezoelectric wafer active sensors (PWAS) may be interrogated at the same time. Automatic data collection systems that permit an operator to perform data acquisition from the all desired sensors by pressing one button are known. In addition, phase-array data processing systems are known that perform NDE through virtual beam forming. U.S. Pat. No. 6,996,480 B2 illustrates such a system. For the latter method, different PWAS array configurations are needed. The increasing number of PWAS for phase-array method means an increasing number of wiring and electronic cross-talking.
While various implementations of structural health monitoring devices and have been developed, and while various methodologies have been proposed to evaluate structural health, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.